The invention relates to a system for measuring the capacitance value of a capacitor, and more particularly, to a system for measuring the capacitance of a capacitive sensor or probe having a parallel resistance component.
With any capacitive sensing system, system accuracy is dependent on the system sensing only the capacitive component of the capacitive probe signal, while ignoring any signal caused by resistive conductance of the probe.
In known systems for measuring the capacitance of a capacitor sensor, a quadrature detection system is employed to eliminate system response to the resistive component of the probe. The ability to reject the resistance signal and detect the capacitance signal using this approach is dependent upon the accuracy of deriving a signal 90.degree. out of phase with the capacitance probe excitation. Even small phase errors of 1.degree. can cause 1% or larger errors in measuring the capacitance value.